Love this guy because it's a classy, discreet way to ask people to sign up for your email list without putting an obnoxious pop-up in their face. You can tell Opt-in Monster to slide in a nice little banner along the bottom of the website with some custom text based on which page they're on at the time, how long they've been on the site, how many pages they've clicked on, and more. It's great if you're serious about growing your list without being an asshole.